From b29693a30b4def57c9c38be4c6f5ff2f9a6e9db9 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Mon, 4 Mar 2019 18:11:26 +0000
Subject: [PATCH] Clean up read-receipt handling.

Remove a call to run_as_background_process: there is no need to run this as a
background process, because build_and_send_edu does not block.

We may as well inline the whole of _push_remotes.
---
 changelog.d/4797.misc        |  1 +
 synapse/handlers/receipts.py | 99 +++++++++++++++---------------------
 2 files changed, 43 insertions(+), 57 deletions(-)
 create mode 100644 changelog.d/4797.misc

diff --git a/changelog.d/4797.misc b/changelog.d/4797.misc
new file mode 100644
index 0000000000..822e98e6a7
--- /dev/null
+++ b/changelog.d/4797.misc
@@ -0,0 +1 @@
+Clean up read-receipt handling.
diff --git a/synapse/handlers/receipts.py b/synapse/handlers/receipts.py
index 8b2d03a756..1728089667 100644
--- a/synapse/handlers/receipts.py
+++ b/synapse/handlers/receipts.py
@@ -16,7 +16,6 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.types import get_domain_from_id
 
 from ._base import BaseHandler
@@ -38,31 +37,6 @@ class ReceiptsHandler(BaseHandler):
         self.clock = self.hs.get_clock()
         self.state = hs.get_state_handler()
 
-    @defer.inlineCallbacks
-    def received_client_receipt(self, room_id, receipt_type, user_id,
-                                event_id):
-        """Called when a client tells us a local user has read up to the given
-        event_id in the room.
-        """
-        receipt = {
-            "room_id": room_id,
-            "receipt_type": receipt_type,
-            "user_id": user_id,
-            "event_ids": [event_id],
-            "data": {
-                "ts": int(self.clock.time_msec()),
-            }
-        }
-
-        is_new = yield self._handle_new_receipts([receipt])
-
-        if is_new:
-            # fire off a process in the background to send the receipt to
-            # remote servers
-            run_as_background_process(
-                'push_receipts_to_remotes', self._push_remotes, receipt
-            )
-
     @defer.inlineCallbacks
     def _received_remote_receipt(self, origin, content):
         """Called when we receive an EDU of type m.receipt from a remote HS.
@@ -128,43 +102,54 @@ class ReceiptsHandler(BaseHandler):
         defer.returnValue(True)
 
     @defer.inlineCallbacks
-    def _push_remotes(self, receipt):
-        """Given a receipt, works out which remote servers should be
-        poked and pokes them.
+    def received_client_receipt(self, room_id, receipt_type, user_id,
+                                event_id):
+        """Called when a client tells us a local user has read up to the given
+        event_id in the room.
         """
-        try:
-            # TODO: optimise this to move some of the work to the workers.
-            room_id = receipt["room_id"]
-            receipt_type = receipt["receipt_type"]
-            user_id = receipt["user_id"]
-            event_ids = receipt["event_ids"]
-            data = receipt["data"]
+        receipt = {
+            "room_id": room_id,
+            "receipt_type": receipt_type,
+            "user_id": user_id,
+            "event_ids": [event_id],
+            "data": {
+                "ts": int(self.clock.time_msec()),
+            }
+        }
 
-            users = yield self.state.get_current_user_in_room(room_id)
-            remotedomains = set(get_domain_from_id(u) for u in users)
-            remotedomains = remotedomains.copy()
-            remotedomains.discard(self.server_name)
+        is_new = yield self._handle_new_receipts([receipt])
+        if not is_new:
+            return
 
-            logger.debug("Sending receipt to: %r", remotedomains)
+        # Work out which remote servers should be poked and poke them.
 
-            for domain in remotedomains:
-                self.federation.build_and_send_edu(
-                    destination=domain,
-                    edu_type="m.receipt",
-                    content={
-                        room_id: {
-                            receipt_type: {
-                                user_id: {
-                                    "event_ids": event_ids,
-                                    "data": data,
-                                }
+        # TODO: optimise this to move some of the work to the workers.
+        data = receipt["data"]
+
+        # XXX why does this not use state.get_current_hosts_in_room() ?
+        users = yield self.state.get_current_user_in_room(room_id)
+        remotedomains = set(get_domain_from_id(u) for u in users)
+        remotedomains = remotedomains.copy()
+        remotedomains.discard(self.server_name)
+
+        logger.debug("Sending receipt to: %r", remotedomains)
+
+        for domain in remotedomains:
+            self.federation.build_and_send_edu(
+                destination=domain,
+                edu_type="m.receipt",
+                content={
+                    room_id: {
+                        receipt_type: {
+                            user_id: {
+                                "event_ids": [event_id],
+                                "data": data,
                             }
-                        },
+                        }
                     },
-                    key=(room_id, receipt_type, user_id),
-                )
-        except Exception:
-            logger.exception("Error pushing receipts to remote servers")
+                },
+                key=(room_id, receipt_type, user_id),
+            )
 
     @defer.inlineCallbacks
     def get_receipts_for_room(self, room_id, to_key):